To provide the plate making apparatus of a printing machine which can make a plate without generating troubles such as deformation and deterioration in dimensional reproducibility even when a master which is formed substantially from a thermoplastic resin film alone without having a master of a thin porous support or a porous support is used.

In a plate making apparatus having a master housing means 11 for housing a master 18, a thermal head 12, a platen roller 13, and a cutting means 16, belt rollers 19a, 19b which can rotate freely on the upstream side and downstream side in the master conveyance direction of the platen roller 13 are provided, and a conveyance belt 20 which contacts the master 18 and conveys it is installed between the platen roller 13 and each belt roller 19a, 19b.